The present invention relates to a sustained-release preparation-capable of releasing a drug for a prolonged period of time. More particularly, the invention relates to a hydrogel-type sustained-release preparation capable of satisfactorily releasing a drug not only in the upper digestive tract but also in the lower digestive tract, particularly in the colon.
A variety of hydrogel-type preparations have heretofore been proposed for realizing sustained release of drugs. For example, JP-A-62-120315 discloses a preparation obtained by compression-molding a drug, a hydrogel-forming water-soluble polymer and an enteric coating base (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d). JP-A-63-215620 discloses a hydrogel-type preparation which comprises a core comprising a drug and a water-soluble polymer and an outer layer comprising a water-soluble polymer as a base. JP-B-40-2053 discloses a sustained-release preparation, or the like, comprising a mixture of a drug and a high polymer of ethylene oxide and, as an optional component, a hydrophilic substance, or the like (the term xe2x80x9cJP-Bxe2x80x9d as used herein means an xe2x80x9cexamined Japanese patent publicationxe2x80x9d).
However, all of these preparations are designed to release a drug continuously while the administered preparation is still retained in the upper digestive tract, typically in the stomach and small intestine, and are not intended to provide for a release of the drug in the lower digestive tract, typically in the colon, where little water is available. Thus, for any sustained-release preparation designed to release a drug for absorption during its descent down in the digestive tract, the extent of drug release and absorption in the upper digestive tract has a major influence on the bioavailability of the drug. However, it is generally believed that the release of the drug in the colon can hardly be expected because of the paucity of water and the influence of spodogenous contents, or the like, and actually, little research has been undertaken on drug release in colon (Phar. Tech. Japan 8 (1), (1992), 41).
Furthermore, the biological half-life of a drug per se is also an important factor in the design of sustained-release preparations. It has been generally considered difficult to design a preparation providing for dramatic sustained release for a drug having a short half-life period (The Pharmaceuticals Monthly 25  (11), (1983), 29).
As a result of extensive studies on the sustained-release of a drug, the inventors of the present invention discovered that the release of a drug in the colon, which is low in water content, can be achieved by providing a preparation adapted to absorb water into its core to undergo substantially complete gelation during its stay in the upper digestive tract such as the stomach and small intestine, and then move in the form of the gel down to the lower digestive tract. The present invention was achieved based on the above finding.
Thus, the present invention relates to a hydrogel-type sustained-release preparation comprising (1) at least one drug, (2) an additive providing for a penetration of water into the core of the preparation, and (3) a hydrogel-forming polymer, which preparation undergoes a substantially complete gelation during its stay in the upper digestive tract such as the stomach and small intestine and is capable of releasing a drug in the colon.
The term xe2x80x9csubstantially complete gelationxe2x80x9d of the preparation as used in this specification refers to the state in which not less than about 70%, preferably not less than about 80%, of the preparation is gelled.
Since even the colon can be utilized as a site of absorption, the sustained-release preparation of the present invention prolongs the absorption period of the drug to a remarkable extent and, hence, insures a steady blood level of the drug. Thus, the preparation of the present invention absorbs water during its stay in the upper digestive tract to undergo a substantially complete gelation and then moves down into the lower digestive tract with its surface being constantly eroded, and maintains drug release by further erosion in the lower digestive tract, with the result that a sustained and sufficient absorption of the drug is achieved even in the colon where little water is available.
The sustained-release preparation of the present invention is described in further detail hereinafter.
The drug or drugs which can be used in the preparation according to the present invention are not particularly limited in kind, provided that they are used for sustained-release system.
Thus, representative examples of the drugs include antiinflammatory, antipyretic, anticonvulsant and/or analgesic agents such as indomethacin, diclofenac, diclofenac Na, codeine, ibuprofen, phenylbutazone, oxyphenbutazone, mepirizol, aspirin, ethenzamide, acetaminophen, aminopyrine, phenacetin, scopolamine butylbromide, morphine, etomidoline, pentazocine, fenoprofen calcium, etc; tuberculostats such as isoniazid, ethambutol hydrochloride, or the like; cardiocirculatory system drugs such as isosorbide dinitrate, nitroglycerin, nifedipine, barnidipine hydrochloride, nicardipine hydrochloride, dipyridamole, amrinone, indenolol hydrochloride, hydralazine hydrochloride, methyldopa, furosemide, spironolactone, guanethidine nitrate, reserpine, amosulalol hydrochloride, or the like; antipsychotic agents such as chlorpromazine hydrochloride, amitriptyline hydrochloride, nemonapride, haloperidol, moperone hydrochloride, perphenazine, diazepam, lorazepam, chlordiazepoxide, or the like; antihistaminic agents such as chlorpheniramine maleate, diphenhydramine hydrochloride, or the like; vitamins such as thiamine nitrate, tocopherol acetate, cycothiamine, pyridoxal phosphate, cobamamide, ascorbic acid, nicotinamide, or the like; antigout agents such as allopurinol, colchicine, probenecid, or the like; hypnotic sedatives such as amobarbital, bromovalerylurea, midazolam, chloral hydrate, or the like; antineoplastic agents such as fluoroauracil, carmofur, aclarubicin hydrochloride, cyclophosphamide, thiotepa, or the like; anticongestants such as phenylpropanolamine, ephedrine, or the like; antidiabetics such as acetohexamide, insulin, tolbutamide, or the like; diuretics such as hydrochlorothiazide, polythiazide, triamterene, or the like; bronchodilators such as aminophylline, formoterol fumarate, theophylline, etc; antitussives such as codeine phosphate, noscapine, dimemorfan phosphate, dextromethorphan, etc; antiarrhythmic agents such as quinidine nitrate, digitoxin, propafenone hydrochloride, procainamide, or the like; surface anesthetics such as ethyl aminobenzoate, lidocaine, dibucaine hydrochloride, or the like; antiepileptics such as phenytoin, etosuximide, primidone, or the like; synthetic adrenocortical steroids such as hydrocortisone, prednisolone, triamcinolone, betamethasone, or the like; digestive system drugs such as famotidine, ranitidine hydrochloride, cimetidine, sucralfate, sulpiride, teprenone, plaunotol, or the like; central nervous system drugs such as indeloxazine, idebenone, tiapride hydrochloride, bifemelane hydrochloride, calcium hopantenate, or the like; hyperlipemia treating agents such as pravastatin sodium or the like; and antibiotics such as ampicillin phthalidyl hydrochloride, cefotetan, josamycin arid so on. A typical drug among the above drugs is nicardipine hydrochloride. Drugs having short biological half-lives can also be utilized. The amount of the drug may be any of pharmaceutically effective amount, but is usually below 85 weight %, and preferably below 80 weight % based on the total weight of the preparation.
In order that these drugs may be readily absorbed in the colon which is low in water content, it is preferable to improve their solubilities in advance. Known techniques for improving the solubility of a drug which can be applied to hydrogel preparation can be employed. Among such techniques (solubilizing treatment) can be mentioned the method comprising adding a surfactant (e.g. polyoxyethylene-hydrogenated castor oils, polyoxy-ethylene-sorbitan higher fatty acid esters, polyoxyethylene polyoxypropylene glycols, sucrose fatty acid esters, or the like) and the method comprising preparing a solid dispersion of the drug and a solubilizer such as a polymer (e.g., a water-soluble polymer such as hydroxypropylmethylcellulose (HPMC), polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), or the like, or an enteric polymer such as carboxymethylethylcellulose (CMEC), hydroxyproplymethylcellulose phthalate (HPMCP), methyl methacrylate-methacrylic acid copolymer (Eudragit L and S; the trade name of Rhom and Haas Co.), or the like). When the drug is basic substance, the method comprising adding an organic acid such as citric acid, tartaric acid or the like can be employed. If necessary, the method involving the formation of a soluble salt or the method comprising forming a clathrate using cyclodextrin or the like can also be employed. These procedures for solubilization can be modified as necessary according to the particular drug.
[xe2x80x9cRecent Manufacturing Pharmacy Technique and its Application Ixe2x80x9d, Isamu Utsumi et al., Medicinal Journal, 157-159 (1983); and xe2x80x9cPharmacy Monograph No. 1, Bioavailabilityxe2x80x9d, Tsuneji Nagai et al., Softscience Co., 78-82 (1988)]
Among these methods, the method comprising preparing a solid dispersion of the drug and a solubilizer is particularly preferred (cf. JP-A-56-49314 and French Patent 2460667).
The additive for allowing water to penetrate into the core of the preparation according to the present invention (this additive for insuring a penetration of water into the preparation core will hereinafter be referred to as xe2x80x9chydrophilic basexe2x80x9d) is such that the amount of water required to dissolve 1 g of the hydrophilic base is not more than 5 ml and preferably not more than 4 ml at the temperature of 20xc2x15xc2x0 C. The higher the solubility of the hydrophilic base in water, the more effective is the base in allowing water into the core of the preparation. The hydrophilic base includes, inter alia, highly hydrophilic polymers such as polyethylene glycol (PEG; e.g. PEG400, PEG1500, PEG4000, PEG6000 and PEG20000, produced by Nippon Oils and Fats Co.) and polyvinylpyrrolidone (PVP; e.g. PVP K30, the trade name of BASF), sugar alcohols such as D-sorbitol, xylitol, or the like, sugars such as sucrose, anhydrous maltose, D-fructose, dextran (e.g. dextran 40), glucose or the like, surfactants such as polyoxyethylene-hydrogenated castor oil (HCO; e.g. Cremophor RH40 produced by BASF, HCO-40 and HCO-60 produced by Nikko Chemicals Co.), polyoxyethylene-polyoxypropylene glycol (e.g. Pluronic F68 produced by Asahi Denka Kogyo K.K.), polyoxyethylene-sorbitan high molecular fatty acid ester (Tween; e.g. Tween 80 produced by Kanto Kagaku K.K.), or the like; salts such as sodium chloride, magnesium chloride., or the like; organic acids such as citric acid, tartaric acid., or the like; amino acids such as glycine, xcex2-alanine, lysine hydrochloride, or the like; and amino sugars such as meglumine.
Preferred ones are PEG6000, PVP, D-sorbitol, or the like.
The proportion of such hydrophilic base depends on the characteristics of the drug (solubility, therapeutic efficacy, or the like) and content of the drug, solubility of the hydrophilic base itself, characteristics of the hydrogel-forming polymer used, the patient""s condition at the time of administration and other factors. However, the proportion may preferably be a sufficient level to achieve a substantially complete gelation during the stay of the preparation in the upper digestive tract. The preparation stays in the upper digestive tract in a different period depending on the species and the individual but in about 2 hours after administration in the case of dogs and in about 4 to 5 hours after administration in the case of human (Br. J. clin. Pharmac, (1988) 26, 435-443). For administration to human, the proportion may preferably be a sufficient level to achieve a substantially complete gelation in about 4 to 5 hours after administration. The proportion of the hydrophilic base is, therefore, generally about 5-80% by weight and preferably about 5-60% by weight based on the total weight of the preparation.
When the content of the hydrophilic base is too small, the necessary gelation into the core of the preparation does not proceed so that the release of the drug in the colon becomes insufficient. On the other hand, when the content of the hydrophilic base is excessive, the gelation proceeds in a shorter time but the resulting gel becomes so fragile that the release of the drug is too fast, thus failing to insure a sufficient sustained release. Moreover, because the amount of the base is large, the product becomes bulky.
The hydrogel-forming polymer mentioned above should have the physical characteristics, inclusive of viscosity in the gelled state, which permit the preparation of the present invention to retain its shape more or less during its travel down to the lower digestive tract, namely the colon, by withstanding the contractile forces of the digestive tract associated with the digestion of food.
The hydrogel-forming polymer which can be used in the preparation of the present invention is preferably a polymer showing a high viscosity on gelation. For example, a polymer showing a viscosity of not less than 1000 cps in 1% aqueous solution (at 25xc2x0 C.) is particularly preferred.
The properties of the polymer depend on its molecular weight. The hydrogel-forming polymer which can be used in the present invention is preferably a substance of comparatively high molecular weight, viz. a polymer having an average molecular weight of not less than 2xc3x97106 and more preferably not less than 4xc3x97106.
Among such polymers are polyethylene oxide (PEO) having a molecular weight of not less than 2xc3x97106 [e.g., Polyox WSR-303 (average mol. wt.: 7xc3x97106; viscosity: 7500-10000 cps, 1% in H2O, 25xc2x0 C.), Polyox WSR Coagulant (average mol. wt.: 5xc3x97106; viscosity: 5500-7500 cps, under the same condition above), Polyox WSR-301 (average mol. wt.: 4xc3x97106; viscosity: 1650-5500 cps, under the same condition above), Polyox WSR-N-60K (average mol. wt.: 2xc3x97106; viscosity: 2000-4000 cps, 2% in H2O, 25xc2x0 C.), all of which are trade names of Union Carbide Co.]; hydroxypropylmethylcellulose (HPMC) [e.g., Metolose 90SH100000 (viscosity: 4100-5600 cps., 1% in H2O, 20xc2x0 C.). Metolose 90SH50000 (viscosity: 2900-3900 cps, under the same condition above), Metolose 90SH30000 (viscosity: 25000-35000 cps, 2% in H2O, 20xc2x0 C.), all of which are trade names of Shin-Etsu Chemicals Co.]; sodium carboxymethylcellulose (CMC-Na) [e.g., Sanlose F-150MC (average mol. wt.: 2xc3x97105; viscosity: 1200-1800 cps, 1% in H2O, 25xc2x0 C.), Sanlose F-1000MC (average mol. wt.: 43xc3x97104; viscosity: 8000-12000 cps, under the same condition above), Sanlose F-300MC (average mol. wt.: 3xc3x97105; viscosity: 2500-3000 cps, under the same condition above), all of which are trade names of Nippon Seishi Co., Ltd.]; hydroxyethylcellulose (HEC) [e.g., HEC Daicel SE850 (average mol. wt.: 148xc3x97104; viscosity: 2400-3000 cps, 1% in H2O, 25xc2x0 C.), HEC Daicel SE900 (average mol. wt.: 156xc3x97104; viscosity: 4000-5000 cps, under the same condition above), all of which are trade names of Daicel Chemical Industries]; carboxyvinyl polymers [e.g., Carbopol 940 (average mol. wt.: ca. 25xc3x97105; B.F. Goodrich Chemical Co.) and so on.
The preferred is a PEO having an average molecular weight of not less than 2xc3x97106. Where a continuous release of the drug over a long time, for example more than 12 hours, is required, a polymer having a higher molecular weight, preferably an average molecular weight of not less than 4xc3x97106, or a higher viscosity, preferably a viscosity of not less than 3000 cps at a concentration of 1% in water at 25xc2x0 C., is preferable.
The above hydrogel-forming polymer may be used singly, or two or more kind(s) of the above hydrogen-forming polymers in mixture may be used. Or, the mixture of two or more kinds of any polymers, which mixture has characteristics suitable for the present invention, may be suitably used for the present invention.
In order to insure a release of the drug in the human colon, it is necessary that a portion of the preparation having undergone gelation still remain in the colon even as late as at least 6-8 hours, preferably at least 12 hours, after administration.
In order to provide a hydrogel-type preparation having such properties, although it depends on the volume of the preparation, the kind of polymer and the properties and amount of the drug and of the additive for insuring a penetration of water into the preparation core, it is generally preferable that the preparation contains 10-95 weight % (preferably, 15-90 weight %) of the hydrogen-forming polymer based upon the preparation weighing less than 600 mg, and one preparation contains not less than 70 mg per preparation and preferably not less than 100 mg per preparation of the hydrogel-forming polymer. If the amount of this polymer is less than the above-mentioned level, the preparation will not tolerate erosion in the digestive tract for a sufficiently long time and a sufficient sustained release may not be achieved.
Regarding the types and proportions of the hydrophilic base and hydrogel-forming polymer (the latter is hereinafter referred to as hydrogel-forming base), their usefulness has been established by the following experiments.
(1) The time course of gelation velocity of the hydrogel-type sustained-release preparation according to the present invention
Sample
100 parts by weight of hydrogel-forming base Polyox WSR-303 (referred to as POLYOX303 hereinafter) blended with 150 parts by weight of hydrophilic base PEG6000 was mixed in a mortar. The mixed composition was compression-molded using an oil press at a compression pressure of 1 ton/punch to provide tablets each measuring 8.0 mm in diameter and weighing 200 mg.
Gelation Test
Using the Pharmacopeia of Japan XII (referred to xe2x80x9cJPxe2x80x9d hereinafter) Disintegration Test Fluid 2, a gelation test was carried out by JP Dissolution Test Method 2 (paddle method) at a paddle speed of 25 rpm. Sample tablets were taken out at predetermined intervals, the gel layer was removed and the diameter (D obs) of the portion not forming a gel was measured. From this D obs value, the gelation index (G) was calculated (Table 1, FIG. 1 and Equation 1).
The xe2x80x9cgelation indexxe2x80x9d as used herein represents the percentage of the portion of the tablet which has undergone gelation. The method of calculating the gelation index is not particularly limited but the following calculation method may be mentioned as an example.
Thus, the test tablet is moistened for a predetermined time, the volume (or weight) of the portion not forming a gel is then measured and the result is subtracted from the volume (or weight) of the tablet before the beginning of the test.
To be specific, the gel layer of the tablet moistened for a predetermined time is removed, the diameter (or thickness) of the portion not forming a gel is then measured and the gelation index is calculated by means of Equation 1. The gelation index may also be calculated by means of Equation 2 given hereinafter.
As an alternative which takes advantage of the difference in strength between the gel layer and non-gel portion, the diameter (or thickness) under a predetermined pressure is assumed to be the diameter (or thickness) of the portion not forming a gel and the gelation index is calculated from Equation 1.
                                          Gelation            ⁢                          xe2x80x83                        ⁢            Index            ⁢                          xe2x80x83                        ⁢                          (                              G                ,                %                            )                                =                                    (                              1                -                                                                            (                                              D                        ⁢                                                  xe2x80x83                                                ⁢                        obs                                            )                                        3                                                                              (                                              D                        ⁢                                                  xe2x80x83                                                ⁢                        ini                                            )                                        3                                                              )                        xc3x97            100                          ⁢                  
                ⁢                  D          ⁢                      xe2x80x83                    ⁢          obs          ⁢                      :                    ⁢                      xe2x80x83                    ⁢                      The  diameter  of  the  portion  not  gelled  after
initiation  of  test                          ⁢                  
                ⁢                  D          ⁢                      xe2x80x83                    ⁢          ini          ⁢                      :                    ⁢                      xe2x80x83                    ⁢                      The  diameter  of  the  preparation  before
initiation  of  test                                              Equation        ⁢                  xe2x80x83                ⁢        1            
Results
The hydrogel tablet containing PEG6000 as a hydrophilic base underwent gelation with its core diameter diminishing progressively at a substantially constant rate. Two hours after the initiation of the test, the hydrogel tablet substantially went through gelation (not less than 80%).
(2) Content of Hydrophilic Base
Samples
One-hundred parts by weight of the hydrogen-forming base POLYOX303 blended with a varying proportion, from 0 to 150 parts by weight, of the hydrophilic base PEG6000 was mixed in a mortar and compression-molded using an oil press at a compression pressure of 1 ton/punch to provide tablets each measuring 8.0 mm in diameter and weighing 200 mg.
Gelation Test
Using JP Disintegration Test Fluid No. 2, the gelation test was performed by JP Dissolution Test Method 2 (paddle method) at a paddle speed of 25 rpm. The tablets were taken out at predetermined intervals, the gel layer was stripped off and the diameter (D obs) of the portion not forming a gel was measured. From the D obs value, the gelation index (G) was calculated (Table 2 and FIG. 2).
Results
It was found that the inclusion of 15 parts by weight (13.0% of tablet weight) of the hydrophilic base PEG6000 resulted in not less than 80% gelation in 2 hours. It was also found that the inclusion of 10 parts by weight (9.1% of tablet weight) of the hydrophilic base PEG6000 resulted in not less than 80% gelation in 4 hours.
(3) Screening of Hydrophilic Bases
Samples
One-hundred parts by weight of the hydrogel-forming base POLYOX303 blended with 100 parts by weight of each test hydrophilic base was mixed in a mortar and compression-molded using an oil press at a compression pressure of 1 ton/punch to provide tablets each measuring 8.0 mm in diameter and weighting 200 mg.
Gelation Test
Using JP Disintegration Test Fluid No. 2, the gelation test was performed by JP Dissolution Test Method 2 (paddle method) at a paddle speed of 25 rpm. The tablets were taken out at 2 hours after initiation of the test and the gel layer was stripped off and the diameter (D obs) of the portion not forming a gel was measured. From the D obs value, the gelation index (G) was calculated (Table 3 and FIG. 3).
Results
When D-mannitol and lactose, which require more than 6 ml of water and 8 ml of water for dissolution of 1 g, were respectively added, the systems showed gelation indices comparable to the index of the system using POLYOX303 alone, indicating that these additives are less effective in causing gelation to proceed into the core of the tablet.
It was found that as the hydrophilic base providing for not less than 80% gelation in 2 hours, highly soluble bases (which require not more than 5 ml, preferably not more than 4 ml, of water for dissolution of 1 gram) such as glycine, PVP K30, PEG6000 and D-sorbitol are suitable.
(4) Studies on Hydrogen-Forming Base
Using acetaminophen and nicardipine hydrochloride (Pd) as model drugs, the proportion and molecular weight of a hydrogel-forming base which are necessary for the sustained-release preparation were investigated.
I. Study of Optimum Proportion
The relationship between the proportion of a hydrogel-forming base and the pattern of dissolution was investigated.
1. Acetaminophen
The components mentioned in Table 4 in the indicated proportions were mixed in a mortar, respectively, and each composition was compression-molded using an oil press at a compression pressure of 1 ton/punch to provide tablets (each containing 50 mg of acetaminophen).
2. Nicardipine Hydrochloride (Pd)
In a mixture of water and methanol (1:9) were dissolved 1 part by weight of Pd, 0.2 part by weight of HCO-60 and 0.4 part by weight of hydroxypropylmethylcellulose (TC-5E, produced by Shin-Etsu Chemical Co.) and the solution was spray-dried using a spray dryer to provide Spray-dried Product 1.
The component materials mentioned in Table 5 in the indicated proportions were respectively mixed in a mortar and each composition was compression-molded using an oil press at a compression pressure of 1 ton/punch to provide tablets (each containing 80 mg of Pd).
Dissolution Test
Using JP Disintegration Test Fluid 1 or 2, the dissolution test was carried out by JP Dissolution Test Method 2 (paddle method) using the acetaminophen and nicardipine hydrochloride (Pd) tablets as models. Sampling was performed at predetermined intervals and the amount of the drug in each sample was determined by the UV method (FIGS. 4 and 5).
Results
It was found that the rate of dissolution could be controlled by varying the proportion of the hydrogel-forming base POLYOX303. It was also found that when 50 mg of acetaminophen was used as the principal agent and not less than 100 mg (50% of tablet weight) of POLYOX303 was added, a sustained release of the drug lasting for not less than 12 hours was realized even under vigorous agitation (paddle speed 200 rpm, pH 6.8). Similarly, when 80 mg of Pd was used as the principal agent, the inclusion of not less than 96 mg (37.5% of tablet weight) of POLYOX303 insured a sustained release lasting for not less than 12 hours even under vigorous agitation (paddle speed 200 rpm, pH 1.2).
The optimum proportion of the hydrogel-forming base depends on the types and amounts of the drug and hydrophilic base and the desired dissolution rate, among other factors, but it was found that the larger was the proportion of the hydrogel-forming base, the greater was the sustainment of release. It was also found that when a sustained release lasting for not less than 12 hours is desired, it is necessary to include not less than about 70 mg, preferably not less than 100 mg, of the hydrogel-forming base per tablet.
II. Study of Relationship between Molecular Weight of Hydrogel-Forming Base and Duration of Release
1. Acetaminophen
As the polyethylene oxide (PEO), those species having average molecular weights of 9xc3x97105, 1xc3x97106, 2xc3x97106, 4xc3x97106, 5xc3x97106 and 7xc3x97106 were used. In each case, the component materials were mixed in a mortar and compression-molded using an oil press at a compression pressure of 1 ton/punch to provide tablets each measuring 9.0 mm in diameter and weighing 350 mg.
2. Nicardipine Hydrochloride (Pd)
In a mixture of water and methanol (1:9) were dissolved 1 part by weight of Pd, 0.4 part by weight of HCO-40 and 0.8 part by weight of hydroxypropylmethylcellulose (TC-5E, produced by Shin-Etsu Chemical Co.) and the solution was spray-dried using a spray dryer to provide Spray-dried Product 2.
As the polyethylene oxide (PEO), those species having average molecular weights of 9xc3x97105, 1xc3x97106, 2xc3x97106, 4xc3x97106, 5xc3x97106 and 7xc3x97106 were used. In each case, the component materials were mixed in a mortar and compression-molded using an oil press at a compression pressure of 1 ton/punch to provide tablets each measuring 11.0 mm in diameter and weighing 568 mg (containing 80 mg of Pd).
Release Test
The acetaminophen- and nicardipine-containing preparations were tested in the same manner as the dissolution test carried out in I. Study of the Optimal Proportion (FIGS. 6 and 7).
Results
The rate of dissolution varied with different average molecular weights of hydrogel-forming base polyethylene oxide (PEO). When 50 mg of acetaminophen was used as the principal agent, the use of PEO with an average molecular weight of not less than 4xc3x97106 resulted in a sustained release lasting for not less than 12 hours under vigorous agitation (paddle speed 200 rpm, pH 6.8).
Similarly, when 80 mg of Pd was used as the principal agent, the use of PEO with an average molecular weight of not less than 2xc3x97106 enabled a sustained release lasting for not less than 12 hours.
(5) Verification of In Vivo Gelation
Samples
The hydrogel-forming base (POLYOX303) and the hydrophilic base (PEG6000, PVP K30, of D-sorbitol) in the ratios indicated below were respectively mixed in a mortar and each mixture was compression-molded using an oil press at a compression pressure of 1 ton/punch to provide tablets each measuring 8.0 mm in diameter and weighing 200 mg.
Autopsy Test in Dogs
Male beagle dogs (Dogs A and B) fasted for about 20 hours were respectively dosed orally with each test preparation, together with 30 ml of water. Two hours later, the animals were anesthetized with pentobarbital Na and, after bleeding, the abdomen was opened. The tablet was recovered from the digestive tract and the D obs value was determined. From the D obs value, the gelation index (G) was calculated (Table 8).
Results
In Dog A, the tablets had already been transported to the colon by 2 hours after administration and the upper digestive tract residence time was less than 2 hours. In contrast, all the tablets except the one containing 10 parts of PEG6000 had already undergone not less than 80% gelation, generally in agreement with in vitro data.
In Dog B, the tablets remained in the stomach at 2 hours after administration and all the tablets had undergone more than 80% gelation.
The above results indicated that hydrogel tablets containing a hydrophilic base providing for not less than 80% gelation in vitro (PVP K30, PEG6000 and D-sorbitol) in appropriate amounts are ready to gel due to penetration of water into the tablet core even in vivo.
If necessary, the preparation of the present invention may include appropriate other pharmaceutically acceptable additives such as vehicles (e.g., lactose, mannitol, potato starch, wheat starch, rice starch, corn starch, and crystalline cellulose), binders (e.g., hydroxylpropylmethylcellulose, hydroxypropylcellulose, methylcellulose, and gum arabic), swelling agents (e.g., carboxymethylcellulose, carboxymethylcellulose calcium, and cross-linking carboxymethylcellulose sodium), lubricants (e.g., stearic acid, calcium stearate, magnesium stearate, talc, magnesium meta-silicate aluminate, calcium hydrogen phosphate, and anhydrous calcium hydrogen phosphate), fluidizers (e.g., hydrous silica, light anhydrous silicic acid, and dried aluminum hydroxide gel), colorants (e.g., yellow iron, sesquioxide and iron sesquioxide), surfactants (e.g., sodium lauryl sulfate, sucrose fatty acid ester), coating agents (e.g., zein, hydroxypropylmethylcellulose, and hydroxypropylcellulose), aromas (e.g., l-menthol, peppermint oil, and fennel oil), preservatives (e.g., sodium sorbate, potassium sorbate, methyl p-benzoate, and ethyl p-benzoate), or the like.
The preparation of the present invention is a solid preparation having a certain shape and hydrogen-forming ability, and can be manufactured by the conventional processes utilized for the production of hydrogel preparations. Typical processes are the compression tabletting comprising blending the drug, hydrophilic base and hydrogel-forming polymer, if necessary with the addition of other additives, and compression-molding the resulting composition; the capsule compression filling; the extrusion molding comprising fusing a mixture and setting the fused mixture; and the injection molding; or the like. Thereafter, any coating treatment such as sugar coating and film coating may be applied or filing into capsules may be carried out.
Solubilization, if performed, of the drug for use in the preparation of the invention can be carried out prior to the above-described manufacturing process. The hydrophilic base according to the present invention may double as said solubilizer in the case that solubilization is carried out. For example, the preparation of the present invention can be manufactured by a process comprising blending the drug, previously solubilized using the hydrophilic base and, if necessary, a different additive, with the hydrogel-forming polymer and, if necessary, other additives, and compression-molding the resulting composition.
If required, the sustained-release preparation of the present invention may have a immediate-release portion. For example, the preparation of the present invention may be provided with such a immediate-release part by way of coating.
Depending on the intended use, the product of the invention can be provided in the form of a dry coated tablet. For example, when a high blood concentration at a definite time after administration is desired, the core tablet is manufactured according to a formulation providing for rapid drug release (with an increased amount of the drug, a reduced amount of the hydrogel-forming base, and/or an increased amount of the hydrophilic base) and, then, the outer layer is formed using a formulation providing for retarded release (with a reduced amount of the drug, an increased amount of the hydrogel-forming base and/or a reduced amount of the hydrophilic base) so that the rate of drug release may be accelerated after a predetermined time.